The technique of bumping and flip-chip bonding is wide spread in the manufacturing of direct conversion x-ray imaging devices. Typically the bumps are grown with electroplating or electroless on the readout substrate side at a wafer scale. Then the wafer is diced and flip-bonded to the detector substrate. The bumps can however be grown on both sides, i.e., on the readout and/or the detector substrate. Typical bump compositions found in imaging devices are PbSn, BiPbSn, BiSn, Au, AgSn, and In. Each has its advantages. Examples of bump-bonded semiconductor radiation imaging devices can be found in U.S. Pat. No. 5,952,646A and U.S. Pat. No. 6,933,505B2. In Nuclear Instruments and Methods in Physics Research Section A Vol 527 Issue 3, Spartiotis et al.: “A CdTe real time X-ray imaging sensor and system”, a detailed embodiment of a CdTe x-ray imaging device is disclosed where the bumps are BiSn, grown on the CMOS. The pixel size is 100 μm (one hundred micrometers) and by way of example the bump size is approximately 25 μm (twenty five micrometers) while the bump is roughly spherical. After the bonding the bumps are squashed and the bump is more like an ellipsoid with post bonding height of about 15 μm (fifteen micrometers). In Nuclear Instruments and Methods in Physics Research Section A Vol 501 Issues 2-3, Spartiotis et al.: “A directly converting high-resolution intra-oral X-ray imaging sensor”, an x-ray imaging sensor for intraoral imaging is disclosed. The readout substrate is again a CMOS and the detector is fully depleted Si. The pixel size in this case is 35 μm (thirty five micrometers). For so small pixel size the bumps are expected to be of the order 10 μm-15 μm and the post bonding height around 10 μm.
In other prior examples, the bumps are grown on both the readout substrate (CMOS) and the detector substrate (Si, CdTe, CdZnTe etc). In such examples one finds In bumps and/or Au studs.
The prior techniques in bump-bonded semiconductor imaging devices work and are efficient due to the relatively large pixel size. By large pixel size is meant pixel pitch of thirty five micrometers (35 μm) to two hundred micrometers (200 μm). At the low end (close to 35 μm) the above described bump bonding techniques suffer from severe limitations:                During bonding the spherical shape of the bump becomes ellipsoid and the bump is squashed and extends laterally. There is a high risk of shorting a bump with its neighboring bump(s).        The surface (active area) of the detector and the CMOS (readout substrate) can be several square cm, and the uniformity of the spherical bumps becomes critical. A non-uniformity of the spherical bump shape of ±3 μm becomes critical in a substrate size of 2 cm×1 cm or larger. The manufacturing ability gets even more compromised for small pixel sizes, i.e., for pixels of 35 μm or less. For such small pixels the spherical bumps need to be 15 μm or smaller and such bumps become increasingly difficult to manufacture over large areas with sufficient uniformity (±3 μm) using conventional electroplating or electroless technique.        For pixel sizes less than 35 μm, the spherical bumps need be of the order of 5 μm-15 μm and as mentioned above making such PbSn, BiSn, AgSn, In (etc) spherical (or almost spherical) bumps of such small size, becomes increasingly difficult, especially given the large area and uniformity constraints.        The current bumps and interconnect technologies in semiconductor direct conversion radiation imaging devices have a deforming structure. This means that the whole bump or bonding element (which may have some other general shape as well) is deformed during the bonding process. As a result there is no “guaranteed” minimum post bonding height. The post bonding height depends on how much the bump (or bonding element) will be deformed, i.e., it depends on the bonding process, the bump size and bump uniformity across the readout substrate.        
It is therefore no coincidence that the breakthrough intraoral sensor described in the above-cited NIM A501 2003 “A directly converting high-resolution intra-oral X-ray imaging sensor”, never came to the market despite the efforts of several sensor manufacturers trying to employ the above mentioned conventional bump bonding techniques. The yield was too low and the manufacturing cost too high.
Furthermore, there are no known direct conversion, bump-bonded, high pixel density x-ray (or gamma ray, beta ray or other form of radiation) imaging devices, at least none produced regularly and with high yield. High pixel density means a readout pixel with size of less than sixty micrometers (<60 μm) and preferably less than thirty five micrometers (<35 μm) bump bonded to a detector pixel with size of less than thirty five micrometers (<35 μm).